US Spec P750 Weber Recalibration

[murphus]

Mike, mine is also 34mm. It'll be a bit before i get around to all of it, but I plan to copy your settings and see how it works. I have different emulsion tubes than you, F36 vs. F44. But as I need new emulsion tubes I'm leaning toward using the F44s that apparently work well on your bike. Will be interesting to see, and I'll certainly report back once I've set it up and run it.

[Mike's bikes]

My bike had a K&N filter element in the standard airbox when I got it. I changed that to an OE type paper element, making sure that it stayed in the sealing channel when the cover was clipped on. That change alone made a noticable difference. I mention it because the aftermarket cotton mesh elements seem ubiquitous.

[Goldstar500]

I’m in the process of trying these settings on my Paso 750 Weber. I’ve just switched the 145 main jet to a 150. The rest of the settings are the same including the 34mm Venturi. I should be able to test it in a few days. It was already running well with no flat spots but I wanted to make sure it wasn’t too lean in the higher rpm.

[Mike's bikes]

Goldstar500, are you changing the auxiliary venturi from the original 3.5 to 4.5, or just the jets? Do you have a BSA Gold Star 500? Coincidentally, I have a 1961 500cc DBD Gold Star.

[Goldstar500]

I haven’t touched the auxiliary venturis. I expect they are are standard though I haven’t checked.

I did the first proper test ride today on the new 150 main jets and it ran great. No hesitation when I opened the throttle fully from low revs in the higher gears. The Weber is so good on the Paso, that I don’t know why people go to the trouble of replacing it when it’s so easily tuned. As a side note, I did the coil ignition relay mod and engine no longer cuts out randomly at idle. You could easily blame the Weber for poor idling if you didn’t know about that mod.

Yes, I’ve got a 1939 M24. It runs great on post war ‘touring’ cams. The DBD would be a great bike too, though I’ve never ridden one. Nice to meet another BSA guy on a Ducati forum!

[murphus]

Well, my adventure into Weberdom just got a little interesting. Ordered up everything I need to rejet/reset, all arrived, oh boy, time to start work. Then discovered whomever last worked on the Weber screwed the fuel/air mixture screws in so friggin tight they actually started to blow out the inside of the throttle bore (see pics). Incredible. I've never seen anyone do that. Is there any chance it's useable like this? Asise from the likelyhood that I won't have shit for control over baseline fuel/air mixture, what will it mean to the rest of the operating range? More than a little bummed as I was excited about returning the Paso to stock. Anyone have a parts carb?

[Goldstar500]

I believe the idle mixture screws are useful only for idle mixture setting. I read about this on a blog for the Weber DCNF from a Ferrari Dino owner. The idle jet itself is really the important one, since it controls from idle to 3000rpm. You might be able to get away with new idle mixture screws.
Here is the DCNF blog:
http://dino246blog.blogspot.com/2014/08 ... s-and.html

[murphus]

Thanks for the link, useful information.

[higgy]

Just a quick input
Keep in mind automotive engines are quite different in their operating range and characteristics. Generally large bores and undersquare,water cooled and lower rpm ranges

[a330us]

Thanks for sharing those jets and changes to the original weber but since so many of us have aftermarket less restrictive mufflers on our bikes what changes to your jets and settings would you make? Thanks Arch.

[ducskii]

I all I just bot a 750 Paso 1994 and am going to try and sort mine out . Thanks for the info . Any new info since may of 2021 ?

[murphus]

1994 Paso 750? Wasn't the last Paso the 1992 907ie?